1. Technical Field
The present disclosure relates to level detectors, and more particularly, to a level detector having a threshold voltage that varies with temperature, an internal voltage generator that includes the level detector, and a semiconductor memory device that includes the internal voltage generator.
2. Discussion of Related Art
A level detector is a circuit for determining whether the voltage level of a specific signal is higher than a threshold voltage and for outputting a signal according to the result of the determination. The level detector is widely utilized for semiconductor devices. For example, the level detector is used to compare the level of an internal voltage generated by an internal voltage generator with the level of a threshold voltage (or a reference voltage). That is, the internal voltage generator increases the internal voltage when the level detector detects that the internal voltage is lower than the threshold voltage (or the reference voltage) and decreases the internal voltage when the level detector detects that the internal voltage is higher than the threshold voltage (or the reference voltage).
The internal voltage generated by the internal voltage generator can be used as a supply voltage for internal circuits of a semiconductor device. That is, the internal voltage may be supplied to a memory cell array in the semiconductor memory device or may be used as a supply voltage for a word line drive circuit or a delay circuit for adjusting the timing of a control signal (e.g., a delay time from the activation of a word line enable signal to the activation of a sense amplifier enable signal).
However, in many applications, the threshold voltage needs to vary with temperature. For example, in a semiconductor memory device, an internal voltage supplied to a delay circuit, which is used to obtain a delay time needed to generate a sense amplifier enable signal after a word line is activated, needs to have a lower level at low temperature than at high temperature to obtain a sensing margin. In this case, a level detector in the internal voltage generator needs to have a lower threshold voltage at low temperature than at high temperature.